It's actually a part of the wing (the covert) that's white, like in my photo here: [link] The coverts in your photo are a light brown. Going by the coverts. No idea what the white back is about... But yeah, I can't really tell by the coverts here but I do think he is male because the females are larger than the males (this is the same for most birds of prey). Another way to tell, if you might remember seeing this at the time, is that when in flight the female looks like this [link] and the male like this [link] (note the difference in the black areas of the under wing). Sexing birds can be very difficult, but I hope this helps!
Apparently (I read this in african geographic, its part of national geographic) the cream back is quite rare, only 6% of the Batts in the park have that colouring I also use the sasol bird book app on ipad with is very helpful. Ive not seen them in flight yet